var stream =require("stream");
const { Z_ASCII } = require("zlib");
var MyReadable = stream.Readable;
var rs = new MyReadable();
var c= 'a'.charCodeAt(0);
rs._read=function(){
    console.log(c);
    if(c<'z'.charCodeAt(0)){
        rs.push(String.fromCharCode(c++));//向rs课读流里加内容
    }else{
        rs.push(null)
    }
}

//将可读流输出一个可写流
rs.pipe(process.stdout)